The present invention concerns polyurethanes for reaction injection molding (RIM) applications. Such polyurethanes are being sought for use in various automobile parts so as to reduce weight. As the physical properties are improved, the applications available for replacement of automobile parts currently made of metal can be increased. Such polyurethane RIM applications are thoroughly discussed in a paper by R. M. Gerkin and F. E. Critchfield, titled "THE PROPERTIES OF HIGH MODULUS RIM URETHANES", presented at the September 26-30, 1977 meeting of the Society of Automotive Engineers and in a paper by W. W. Ludwico and R. P. Taylor titled "THE BAYFLEX 110 SERIES-THE NEW GENERATION OF RIM MATERIALS" presented at the same meeting.
One such property which is desirable is to decrease the difference in flexural modulus values as measured at high and low temperatures. The Gerkin and Critchfield article revealed a ratio of the flexural modulus value measured at -23.degree. C. divided by the value measured at 70.degree. C. for unfilled formulations of 5.75 (230.div.40), 5.45 (316.div.58) and 6.83 (205.div.30) see pages 3 and 5. The Ludwico and Taylor paper disclosed ratios of flexural modulus values on unfilled systems measured at -30.degree. C. and 65.degree. C. of 3.56 (64.div.18) see Table I.
We have now discovered polyurethanes useful in RIM applications which have ratios of the flexural modulus values measured on unfilled systems at -20.degree. F. and 158.degree. F. of less than about 3, preferably less than about 2 and such polyurethanes also have at least 2 and preferably at least 3 thermal transition temperatures as measured by thermomechanical analysis between -100.degree. C. and the decomposition temperature of the polyurethane.